An Extensive Survey on Various Query Optimization Techniques

As the database management field has diversified to consider settings in which queries are increasingly complex, statistics are less available, or data is stored remotely, there has been an acknowledgment that the available optimization techniques are insufficient. This has led to a plethora of new techniques, generally placed under the common banner of optimizing complex queries that focus on rewriting the complex queries in a simple manner. Query optimization is the bottleneck of database application performance especially those which store history i.e. data warehouse. SQL is used as query language because most data warehouses are based on relational or extended relational database system. In this survey paper, we identify many of the common issues, themes, and approaches that pervade this work, and the settings in which each piece of work is most appropriate. Our goal with this paper is to be a ―value-add‖ over the existing papers on the material, providing not only a brief overview of each technique, but also a basic framework for understanding the field of query processing in general and also to reduce the complexity of the queries to enhance the query processing and optimization engines. Keywords— Data warehouse, query optimization, query processing, complex queries, SQL.